Method and apparatus for producing extreme ultra-violet light for use in photolithography

ABSTRACT

A method and apparatus for producing extreme ultra-violet light comprising a nozzle for flowing a gas at a supersonic velocity, a source for directing a radiated energy beam into the flowing gas to stimulate emission of extreme ultra-violet light therefrom, and a diffuser for capturing a substantial portion of the gas so as to mitigate contamination caused thereby. The extreme ultra-violet light so produced is suitable for use in photolithography for integrated circuit fabrication and the like.

FIELD OF THE INVENTION

The present invention relates generally to photolithographic techniquesand apparatus for use in the fabrication of semi-conductor componentsand more particularly to a method for producing extreme ultra-violetlight for use in a photolithography system for facilitating theproduction of semi-conductor components having geometries of 10 nm andsmaller.

BACKGROUND OF THE INVENTION

The use of photolithographic techniques in the fabrication ofsemi-conductor components such as dynamic RAM chips (DRAM), is wellknown. In the practice of such photolithographic techniques, light isutilized to cure or harden a photomask which prevents the chemicaletching of various semi-conductor, conductor, and insulator portions ofthe device, as desired.

As those skilled in the art will appreciate, the trend is towardsemi-conductor components having greater and greater densities. This isparticularly true in the area of memory, wherein it is extremelydesirable to provide as much memory as possible in a given package.

As those skilled in the art will appreciate, it is necessary to decreasethe line size or geometry of the various semi-conductor, conductor, andinsulator lines formed upon the component substrate in order tofacilitate such increased density. That is, by making the individualdevices, i.e., transistors, diodes, etc., formed upon the integratedcircuit chip smaller, a larger number of such devices may be formedthereon. This, of course, facilitates fabrication of DRAM chips havinggreater capacity, for example.

However, when utilizing photolithographic techniques, the lower limit onthe line size is defined by the wavelength of the light utilized in thephotolithographic process. Thus, extreme ultra-violet light (EUV) iscapable of forming smaller line sizes (resulting in greater packagingdensities) than is ultra-violet or visible light. Because of this, it ishighly desirable to utilize extreme ultra-violet light in thephotolithographic processes associated with the fabrication ofintegrated circuit components.

According to contemporary methodology, two important goals associatedwith the use of extreme ultra-violet light in such photolithographicprocesses tend to be mutually exclusive. As those skilled in the artwill appreciate, it is desirable to provide an intense source of extremeultra-violet light and it is also desirable to minimize the generationof debris during the generation of such light.

The curing time is directly proportional to the intensity of the lightsource. Thus, it is desirable to have an intense light source such thatmask curing time may be reduced and the production rate correspondinglyincreased.

It is desirable to minimize the generation of debris since such debrisundesirably absorbs the extreme ultra-violet radiation prior to itsbeing utilized in the curing process. Such debris also undesirablycontaminates and degrades the performance of the optics which areutilized to collect and focus the extreme ultra-violet light. It alsoincreases the vacuum pumping and filtering load on the system.

The generation of such debris is inherent to contemporary methodologiesfor producing extreme ultra-violet light and tends to increase as anattempt is made to increase the intensity of the extreme ultra-violetlight.

According to one exemplary contemporary methodology for generatingextreme ultra-violet light, a radiated energy beam such as the output ofa high energy laser, electron beam, or arc discharge is directed onto aceramic, thin-film, or solid target. Various different solid targetshave been utilized. For example, it is known to form such targets oftungsten, tin, copper, and gold, as well as sold xenon and ice.

The low reflectivity of mirrors which are suitable for use at thedesired extreme ultra-violet light wavelength inherently reduces thetransmission of extreme ultra-violet light through the optical systemand thus further necessitates the use of a high intensity extremeultra-violet light source. Degradation of the mirrors and other opticalcomponents by contamination due to debris formed during the extremeultra-violet light generation is thus highly undesirable. Of course, asthe intensity of the extreme ultra-violet light generation process isincreased (by increasing the intensity of the radiated energy beamdirected onto the target), more debris are formed. Thus, when utilizingsuch solid target configurations, the goals of debris reduction andintensity enhancement tend to be mutually exclusive.

Consequently, the use of lasers and/or electron beams to ionize a gasflow so as to emit the desired intensity of extreme ultra-violet lightwhile mitigating the production of undesirable debris is presently beinginvestigated. Thus, it is known to utilize gas jets for the targets oflasers and electron beams in the production of extreme ultra-violetlight. It is also known to cryogenically cool noble gases such as xenonand argon, so as to cause the gas to assume a super cooled state,wherein the individual atoms are drawn together into large clusters ofseveral thousand atoms or more. While the use of such gas jets and/orcryogenic cooling methodologies have proven generally suitable forlaboratory demonstrations, the vacuum pumping requirements necessary forsuch steady-state operation at high extreme ultra-violet lightproduction rates is economically prohibitive.

As such, it is desirable to provide means for producing high intensityextreme ultra-violet light while minimizing the undesirable productionof debris. It is further desirable to accomplish such extremeultra-violet light production utilizing methodology which substantiallyreduces the vacuum pumping requirements, thereby correspondinglyreducing the size, cost, and power requirements of the system.

SUMMARY OF THE INVENTION

The present invention specifically addresses and alleviates theabove-mentioned deficiencies associated with the prior art. Moreparticularly, the present invention comprises a method and apparatus forproducing extreme ultra-violet light. The method comprises the steps offlowing a gas at a supersonic velocity, directing a radiated energy beaminto the flowing gas to stimulate emission of extreme ultra-violet lighttherefrom, and capturing a substantial portion of the gas so as tomitigate contamination caused thereby. By capturing a substantialportion of the gas, the amount of debris available to contaminate thesystem's optical components is mitigated.

As used herein, the term debris is defined to include any atoms,molecules, electrons, ions, or other material which is a component ofthe flowing gas or which results from the interaction of the flowing gasin the radiated energy beam. As those skilled in the art willappreciate, a substantial portion of such debris is trapped within thegas flow jets, which itself is then captured so as to preventcontamination.

The step of flowing a gas at a supersonic velocity preferably comprisesflowing a pressurized gas through a converging-diverging nozzle, so asto increase the velocity thereof. The converging-diverging nozzlepreferably has a generally rectangular cross-section. Theconverging-diverging nozzle also preferably has a length substantiallygreater than the width thereof (a high aspect ratio).

According to the preferred embodiment of the present invention, both thenozzle from which the supersonic gas flows and the opening in thediffuser into which the supersonic gas is received are approximately 9mm long and approximately 0.9 mm wide, thus giving both an aspect ratioof approximately 10. The diffuser preferably comprises a convergingportion proximate the opening thereof having walls angled atapproximately 6° to the gas flow axis thereof, so as to generate astable system of shocks. The shocks decrease the velocity of the gaswithin the diffuser and increase the pressure thereof, as discussed indetail below.

Those skilled in the art will appreciate that the dimensions of thenozzle and the diffuser may be varied substantially, as desired.Moreover, the throat area, inlet to throat area ratio, throat length,and exit divergence angle of the diffuser are preferably optimizedaccording to well known principles for a given jet in order to obtaindesirable pressure recovery and minimize gas bypass (gas not receivedwithin the diffuser) of the diffuser.

The step of flowing a gas at a supersonic velocity preferably comprisesexpanding the gas so as to substantially decrease the temperaturethereof. As those skilled in the art will appreciate, decreasing thetemperature of the gas substantially increases a density thereof, bycausing the atoms or molecules of the gas to tend to clump together,preferably in large clusters thereof. As those skilled in the art willfurther appreciate, the density increase due to such clumpingsubstantially enhances the emission of extreme ultra-violet lighttherefrom.

According to the preferred embodiment of the present invention, the gascomprises a noble gas, preferably argon, helium, and/or xenon. The gasis preferably flowed at a velocity of at least Mach 2, preferably Mach3.

The gas is preferably flowed at a supersonic velocity through a vacuumchamber, so as to facilitate photolithography, such as in thefabrication of integrated circuit components. The radiated energy beampreferably comprises either an electron beam, a laser beam, or amicrowave beam. Those skilled in the art will appreciate that variousother forms of radiated energy may likewise be suitable.

According to the preferred embodiment of the present invention, theradiated energy beam is directed proximate the converging-divergingnozzle from which the gas flows, such that the radiated energy beampasses through the flowing gas in a manner which mitigates absorption ofthe extreme ultra-violet light stimulated thereby back into the flowinggas. Thus, according to the preferred embodiment of the presentinvention, reabsorption of the stimulated extreme ultra-violet light,particularly by the flowing gas, is minimized. In order to accomplishthis, the radiated energy beam is directed through the flowing gasproximate a surface thereof, so as to reduce the distance that theextreme ultra-violet light stimulated thereby must travel through theflowing gas. It will be appreciated that the amount of gas through whichstimulated extreme ultra-violet light must travel is proportional to thedistance between the point of emission, i.e., the point of interactionbetween the radiated energy beam and the flowing gas, and the outer edgeor surface of the flowing gas, beyond which the extreme ultra-violetlight passes substantially only through vacuum.

Thus, by positioning the radiated energy beam such that it passesthrough the flowing gas proximate a surface thereof, extremeultra-violet light stimulated by the radiated energy beam within theflowing gas travels through less of the flowing gas than would be thecase if the radiated energy beam were positioned deeper inside theflowing gas.

According to the present invention, a substantial portion of the gas isreceived within a diffuser which is configured to reduce the velocity ofthe gas and also to increase the pressure thereof. Thus, the diffusermitigates the contamination of system optical component by reducing theamount of gas flowing within the vacuum chamber. The use of the diffuseralso reduces the load upon the vacuum pump by reducing the pumpingrequirements thereof.

Further, according to the methodology of the present invention, the gascaptured by the diffuser is recycled such that it repeatedly flows fromthe nozzle and is repeatedly stimulated to provide extreme ultravioletlight. Further, according to the preferred embodiment of the presentinvention, that gas removed from the vacuum chamber by the vacuum pumpis also recycled.

The aspect ratio of the cross-section of the diffuser, a the openingthereof, is preferably similar to and approximate that of the aspectratio of the cross-section of the converging-diverging nozzle, at theexit thereof from which the gas flows. Alternatively, the aspect ratioof the cross-section of the diffuser, at the opening thereof, may bedifferent from that of the aspect ratio of the cross-section of theconverging-diverging nozzle at the exit thereof. For example, theopening of the diffuser may optionally be substantially larger incross-sectional area than the exit of the converging-diverging nozzle,so as to enhance the capture of the flowing gas. As those skilled in theart will appreciate, when the cross-sectional area of the opening of thediffuser is substantially larger than the cross-sectional area of theexit of the converging-diverging nozzle, then the aspect ratio of theopening of the diffuser becomes less critical.

Thus, according to the methodology of the present invention, asubstantial portion of the kinetic energy of the gas is converted intopressure, so as to facilitate more efficient recycling thereof. As thoseskilled in the art will appreciate, the gas must be provided to thenozzle at a substantial pressure, so as to effect supersonic flowthereof. By converting a substantial portion of the kinetic energy ofthe gas into pressure, the pumping requirements of the system aresubstantially reduced, thereby reducing the costs of constructive andoperating the system. The pumping requirements are substantially reducedsince the difference between the input and output pressure of the pumpis reduced when the input pressure is increased, as by converting asubstantial portion of the kinetic energy of the gas flow into pressure.

The gas captured by the diffuser, and optionally the gas removed by thevacuum pump as well, is compressed, so as to increase the pressurethereof to that pressure required for achieving the desired gas flowspeed from the nozzle. Heat is removed from the gas prior to its beingprovided to the nozzle, so as to facilitate the desired cooling thereofupon expansion as the gas exits the nozzle.

According to the preferred embodiment of the present invention, thediffuser comprises at least one knife edge which is configured so as toreduce the velocity of the gas captured thereby. As those skilled in theart will appreciate, various different configurations of such knifeedges are suitable for reducing the velocity of the gas captured by thediffuser. For example, the knife edges may comprise concentric,generally parallel sets thereof, having generally rectangular, round, oroval shapes, for example. Alternatively, the knife edges may comprise aplurality of generally horizontal or vertical members. It is alsocontemplated that one or more point-type knife edges, configuredgenerally as pointed needles may alternatively be utilized to generateshock waves.

Thus, according to the present invention, the nozzle and diffuser inletare configured to utilize gas dynamics properties of a supersonic jet ofgas to direct debris formed during interaction of the radiated energybeam and the gas jet into the diffuser, and thus mitigate contaminationof the system's optical components thereby. In this manner thecollecting and focusing optics, for example, are maintained in asubstantially contamination free manner, so as to enhance the integratedcircuit fabrication process performed therewith. As those skilled in theart will appreciate, by reducing the contamination of such opticalcomponents, maintenance, i.e., cleaning, of the system's opticalcomponents, is substantially reduced and the production rate isincreased, thereby providing a substantial economic advantage.

Collecting and focusing optics collect the extreme ultra-violet lightand focus the extreme ultra-violet light upon the desired target, e.g.,a mask being cured upon the integrated circuit component(s) beingfabricated.

Thus, the methodology and apparatus of the present invention providesmeans for producing extreme ultra-violet light in an photolithographysystem for facilitating the production of semi-conductor componentshaving geometries of 10 nm (nanometers) and smaller. According to thepresent invention, means for producing high-intensity extremeultra-violet light while minimizing the undesirable production of debrisare provided. Such extreme ultra-violet light production is furtheraccomplished utilizing methodology which substantially reduces thevacuum pumping requirements, thereby correspondingly reducing the size,cost, and power requirements for the system.

These, as well as other advantages of the present invention will be moreapparent from the following description and drawings. It is understoodthat changes in the specific structure shown and described may be madewithin the scope of the claims without departing from the spirit of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the extreme ultra-violetphotolithography system for facilitating the prodtion of semi-conductorcomponents having geometries of 10 nm and smaller, and showing apressure profile for the flowing gas exiting the converging-divergingnozzle thereof;

FIG. 2 is a perspective view of the converging-diverging nozzle of thepresent invention;

FIG. 3 is a perspective view of the diffuser of the present invention;

FIG. 4 is a perspective view showing gas flowing from theconverging-diverging nozzle into the diffuser and also showing aradiated energy beam stimulating the emission of extreme ultra-violetlight from the flowing gas, a portion of the extreme ultra-violet lightbeing collected and focused by system optics;

FIG. 5 is an enlarged view of a set of knife edges configured asconcentric rectangular members for reducing the speed of the incominggas while simultaneously increasing the pressure thereof;

FIG. 6 is an exploded perspective view of the rectangular knife edges ofFIG. 5;

FIG. 7 is an end view of the converging-diverging nozzle which isconfigured as a flange or cap so as to easily attach to a pulsegenerator;

FIG. 8 is a side view of the converging-diverging nozzle of FIG. 7;

FIG. 9 is a detailed cross-sectional profile of the diverging portion ofthe converging-diverging nozzle;

FIG. 10 is a detailed cross-sectional profile of the diffuser; and

FIG. 11 shows the calculated density field of an extreme ultra-violetlight source jet and diffuser using xenon gas and showing the shockresulting from the supersonic gas flow impinging upon the inner walls ofthe diffuser.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The detailed description set forth below in connection with the appendeddrawings is intended as description of the presently preferredembodiment of the invention and is not intended to represent the onlyform in which the present invention may be constructed or utilized. Thedescription sets forth the functions and the sequence of steps forconstructing and operating the invention in connection with theillustrated embodiment. It is to be understood, however, that the sameor equivalent functions and sequences may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the invention.

The extreme ultra-violet photolithography system for facilitatingproduction of semi-conductor components having geometries of 10 nm andsmaller of the present invention is illustrated in FIGS. 1-11, whichdepict a presently preferred embodiment thereof. Referring now to FIG.1, the extreme ultra-violet photolithography system generally comprisesa converging-diverging nozzle 10 from which gas 11 flows, at asupersonic velocity, toward diffuser 12 which captures a substantialportion of the flowing gas 11. The converging-diverging nozzle 10 andthe diffuser 12, as well as the collecting and focusing optics 29 andthe work piece, i.e., integrated circuit chip(s) being fabricated, areall preferably disposed within a common vacuum chamber 40, so as tofacilitate integrated circuit fabrication utilizing photolithography.

As described in detail below, the diffuser 12 reduces the velocity ofthe flowing gas 11, while simultaneously increasing the pressurethereof. Gas flows from the diffuser 12 via conduit 13 to compressor 14,which preferably comprises a 0.71 hp compressor. The compressor 14compresses, i.e., increases the pressure of, the gas 11 such that it maybe recycled to the converging-diverging nozzle 10 and thus usedrepeatedly to produce extreme ultra-violet light. Gas flows from thecompressor 14 to heat exchanger 16, preferably a 64.1 btu/min heatexchanger for removing heat from the compressed gas.

According to the preferred embodiment of the present invention, thetemperature of the gas entering the heat exchanger 16 is approximately610° K and the temperature of the gas exiting the heat exchanger 16 isapproximately 300° K. The gas exiting the heat exchanger 16 iscommunicated via conduit 17 to the converging-diverging nozzle 10 wherea stagnation pressure of 6,079 torr is developed. Stagnation pressure isdefined herein as that gas pressure when no flow occurs.

Referring now to FIG. 2 also, the converging-diverging nozzle 10 moreparticularly comprises a pressure plenum 18 into which the compressedgas from the heat exchanger 16 flows. The converging-diverging nozzle 10further comprises a converging portion 20 and a diverging portion 22.The converging-diverging nozzle 10 is configured so as to accelerate thegas flowing therethrough to a supersonic velocity, preferably above Mach2, preferably approximately Mach 3.

The diverging portion 22 preferably has a generally rectangularcross-section and is preferably configured such that the length,Dimension L, is substantially greater than the width, Dimension W,thereof. This configuration provides a high aspect ratio whichfacilitates the exposure of a substantial portion of the flowing gas tothe radiated energy beam and which provides a short path for extremeultra-violet light stimulated thereby through the flowing gas.

Referring now to FIGS. 1 and 3, the diffuser 12 generally comprises anopening which corresponds generally in size and configuration to that ofthe widest portion of the diverging portion of the converging-divergingnozzle 10. Thus the opening of the diffuser has a length which ispreferably slightly longer than the length of the converging-divergingnozzle 10 and has a width which is preferably slightly longer than thewidth of the converging-diverging nozzle, so as to capture a substantialportion of the gas flowing from the converging-diverging nozzle 10.Those skilled in the art will appreciate that various differentconfigurations of the diffuser 12 are suitable.

The diffuser decreases in cross-sectional area from the opening 30thereof to the coupling end 32 thereof, at which the fluid conduit 13attaches. As discussed in detail below, the cross-sectional area of thediffuser 12 optionally increases again, from the narrowest portionthereof, so as to define a throat. Such tapering or narrowing of thecross-sectional area of the diffuser 12 provides a gradual slowing ofthe gasses captured thereby, while minimizing the occurrence ofundesirable regurgitation which might otherwise occur.

Optionally, one or more knife edges are formed in or proximate thediffuser 12, so as to aid in the deceleration of the gasses entering theopening 30. According to the preferred embodiment of the presentinvention, the periphery of the opening 30 of the diffuser 12 is formedas a first knife edge 31. Additional concentric generally rectangularknife edges 33 and 35 are disposed within the opening 30 of the diffuser12 and mounted thereto via any suitable means. Knife edge struts mayoptionally be utilized to mount the second 33 and third 35 concentricrectangular knife edges in place within the opening 30 of the diffuser12. Those skilled in the art will appreciate that various differentnumbers and configurations of such knife edges may be utilized to effectgeneration of shocks which tend to decrease the velocity of thesupersonic gas while simultaneously increasing the pressure thereofwithin the diffuser 12.

Isobaric pressure profiles of the gas flowing from theconverging-diverging nozzle 10 are provided in FIG. 1. As shown, theradiated energy beam, an electron beam according to the preferredembodiment of the present invention, is directed into that portion ofthe flowing gas 11 proximate the converging-diverging nozzle 10, so asto enhance the efficiency of the present invention. This is better shownin FIG. 4 which illustrates the relative positions of the electron beam23 and the flowing gas 11 in perspective.

A portion of the extreme ultra-violet light 27 whose emission isstimulated from the flowing gas 11 by the radiated energy beam 23 iscollected and focused by collecting and focusing optics 29, which directthe extreme ultra-violet light onto a work piece, i.e., an integratedcircuit component being fabricated, as desired.

According to the preferred embodiment of the present invention, a vacuumpump, preferably that vacuum pump 36 utilized to evacuate the vacuumchamber 40 within which the gas 11 flows and within which thephotolithographic process is performed, evacuates a substantial portionof the gas 11 which is not captured by the diffuser 12 and provides thatgas 11 back to the converging-diverging nozzle 10, preferably via thecompressor 14 and heat exchanger 16, so as to facilitate recyclingthereof.

Referring now to FIG. 4, in operation a gas, preferably a noble gas suchas argon, helium, or xenon, or a combination thereof, flows at asupersonic velocity from the converging-diverging nozzle 18 when apressurized supply thereof is provided to the converging-divergingnozzle 18 via gas conduit 17. Sufficient pressure is provided bycompressor 14 to achieve the desired gas flow speed.

A radiated energy beam, preferably an electron beam, is directed throughthe supersonic gas flow 11 at a position which minimizes thetransmission of the resulting extreme ultra-violet light through the gas11, thereby mitigating undesirable absorption thereof.

A substantial portion of the flowing gas 11 is captured by the diffuser12 and recycled. A substantial portion of the gas not captured by thediffuser 12 is evacuated from the vacuum chamber 40 via vacuum pump 36and recycled.

At least a portion of the extreme ultra-violet light 27 emitted due tothe interaction of the radiated energy beam 23 with the supersonic gas11 is collected and focused by collecting and focusing optics 29 so asto facilitate photolithography therewith.

Thus, according to the present invention, contamination of thecollecting and focusing optics 29, as well as any other sensitivesurfaces within the vacuum chamber 40, is mitigated. Such contaminationis mitigated since supersonic flow of the gas 11 tends to force all ofthe gas particles, i.e., molecules, atoms, ions, electrons, etc., intothe diffuser 12, thereby substantially mitigating the amount of suchparticles floating freely within the vacuum chamber 40 and capable ofcoming into contact with such sensitive items.

The present invention takes advantage of the gas dynamic properties ofthe supersonic jet to direct any debris generated during the plasmaformation into the diffuser, and thus away from the collection andfocusing optics 29, as well as the rest of the photolithography system.

The efficiency of the present invention is enhanced by minimizing theamount of gas 11 through which the generated extreme ultra-violet light27 must pass. As those skilled in the art will appreciate, extremeultra-violet light is readily absorbed (and thus attenuated) by thenoble gasses from which its emission is stimulated. Thus, it is verydesirable to minimize the distance through which the extremeultra-violet light 27 must travel through such gas. This is accomplishedby positioning the radiated energy beam 23 close to the surface of theflowing gas 11, preferably by positioning the radiated energy beam 23proximate the converging-diverging nozzle 10 where the gas flow has acomparatively narrow cross-sectional area and comparatively highdensity.

Thus, according to the present invention, the high density gas region isconfined to nearly the same volume as that occupied by the radiatedenergy beam. Thus, extreme ultra-violet light generated thereby is notrequired to travel through a substantial portion of the high density gasafter leaving the area where stimulated emission occurs.

The high aspect ratio configuration of the converging-diverging nozzletends to maximize the volume of flowing gas available for interactionwith the radiated energy beam, while simultaneously minimizing thevolume of flowing gas which attenuates the stimulated extremeultra-violet light.

As those skilled in the art will appreciate, the higher the velocity ofthe flowing gas 11, the smaller the mass flow thereof which will divergeor turn away from the gas flow, i.e., jet, when surrounded by the verylow pressure of the vacuum chamber. Any such flow which diverges fromthe gas jet into the high vacuum surrounding the gas jet must ultimatelybe pumped out against a very high adverse pressure ratio, which addssubstantially to the cost of manufacturing and maintaining the system.Even more important, the gas that diverges from the gas jet becomes apotential contaminant for the collecting and focusing optics and alsobecomes an undesirable attenuating mass for the extreme ultra-violetlight which is produced by the interaction of the radiated energy beamand the gas flow.

Further, by converting a significant portion of the kinetic energy ofthe flowing gas 11 into pressure, the need to increase the pressure ofthe gas via the compressor 14 is reduced, thereby facilitating operationwith a smaller capacity and less expensive compressor 14.

Referring now to FIGS. 5 and 6, the generally rectangular concentricknife edges 33, 35 of FIG. 3 are shown in further detail. Each generallyconcentric knife edge 33, 35 preferably comprises a body 37 and a bevel39. As those skilled in the art will appreciate, it is the purpose ofeach knife edge 31, 33, and 35 to produce a shock wave, similar innature to the sonic boom shock wave associated with supersonic aircraft,which defines a region of increased pressure within the diffuser 12, andthus facilitates reduction of the speed of the flowing gas 11 andsimultaneously facilitates an increase in the pressure thereof.

Referring now to FIG. 8, the converging-diverging nozzle is optionallyconfigured as a cap 10a which is specifically sized and shaped to fit astandard pulse generator. Thus, the cap 10a comprises a body 50 which issized to be received within the exit orifice of a pulse generator and aflange 52 which functions as a stop to limit insertion of the body 50into the exit orifice. A rectangular boss 54 has a rectangular opening56 formed therein. The converging-diverging bore 58 of the nozzle isformed in a continuous or co-extensive manner in the body 50, flange 52,and boss 54. Such construction facilitates easy removal and replacementof the converging-diverging nozzle 10a, particularly when a standardpulse generator is utilized.

Referring now to FIG. 9, a preferred cross-sectional profile of a nozzleorifice is shown. The nozzle comprises a converging region 60 whichdecreases to form a neck 62 and then increases in cross-sectional areato form the diverging region 64 thereof. The exit plane 66 is that planeof the nozzle flush with the end thereof, i.e., the outer openingthereof.

Referring now to FIG. 10, the cross-sectional profile of the diffuser isshown. According to the present invention, the diffuser tapers orconverges from the entry plane 70 to define a converging portion 72thereof. At the end of the converging portion 72 a neck 74 is formed andthe diffuser may then optionally diverge or increase in cross-sectionalarea so as to form a diverging portion 76. As those skilled in the artwill appreciate, the velocity of the flowing gas 11 decreases within theconverging portion 72, while the pressure thereof simultaneouslyincreases.

Referring now to FIG. 11, the calculated density field for a xenonextreme ultra-violet light source jet and diffuser is shown. Gas 11afrom within the converging-diverging nozzle exits therefrom at the exitplane 66 to form gas jet 11b. The gas jet 11b enters the diffuser at theentry plane 70 thereof. Within the diffuser 12 first oblique shocks 80are formed due to the knife edge(s) 31 defined by the opening 30 of thediffuser 12. The oblique shocks 80 interact to form perpendicular shock82 downstream therefrom. Second oblique shocks 84 are formed as theflowing gas interacts with the internal walls of the diffuser. Thesecond oblique shocks 84 interact with one another so as to formperpendicular shock 86. Third oblique shocks 88 are formed in a similarmanner downstream from the second oblique shocks 84. As those skilled inthe art will appreciate, each shock defines a high pressure regionwithin which the flowing gas slows. In this manner a plurality of knifeedges may be utilized to form shocks so as to effect slowing of the gasflow and increasing the pressure thereof.

It is understood that the exemplary method and apparatus for producingextreme ultra-violet light described herein and shown in the drawingsrepresents only a presently preferred embodiment of the invention.Indeed, various modifications and additions may be made to suchembodiment without departing from the spirit and scope of the invention.For example, various sizes, shapes, crosssectional configurations, etc.of the nozzle and diffuser are contemplated. It must further beappreciated that various different configurations of the radiated energybeam, other than circular as shown, may be utilized. For example, theradiated energy beam 23 may alternatively be elliptical, square,rectangular, triangular, etc. It is generally desirable that theradiated energy beam 23 be comparable in cross-sectional area to thatportion of the flowing gas 11 proximate the converging-diverging nozzle10, so as to minimize the amount of gas 11 through which stimulatedextreme ultra-violet light 27 must flow. Further, it must be appreciatedthat the method and apparatus for producing extreme ultra-violet lightaccording to the present invention may be utilized in a variety ofdifferent applications, and is not limited to use in photolithographicapplications. Further, it must also be appreciated that the generalmethod and apparatus of the present invention may alternatively beutilized to produce wavelengths of electromagnetic radiation other thanextreme ultra-violet, and thus is not limited to the production ofextreme ultra-violet light.

Thus, these and other modifications and additions may be obvious tothose skilled in the art and may be implemented to adapt the presentinvention for use in a variety of different applications.

What is claimed is:
 1. A method for producing extreme ultra-violetlight, the method comprising:flowing a gas at a supersonic velocity byflowing the gas through a converging-diverging nozzle; directing aradiated energy beam into the flowing gas to stimulate emission ofextreme ultra violet light from the gas; and capturing a substantialportion of the gas so as to mitigate contamination caused by the gas. 2.The method as recited in claim 1 wherein the step of flowing a gas at asupersonic velocity comprises flowing a gas at a supersonic velocitythrough a converging-diverging nozzle having a generally rectangularcross-section.
 3. The method as recited in claim 1 wherein the step offlowing a gas at a supersonic velocity comprises flowing a gas at asupersonic velocity through a converging-diverging nozzle having agenerally rectangular cross-section and also having a lengthsubstantially greater than a width of the cross-section.
 4. The methodas recited in claim 1 wherein the step of flowing a gas at a supersonicvelocity comprises flowing a gas at a supersonic velocity through aconverging-diverging nozzle having an aspect ratio of approximately 10to
 1. 5. The method as recited in claim 1 wherein the step of flowing agas at a supersonic velocity comprises expanding the gas so as tosubstantially decrease a temperature of the gas, and thus substantiallyincrease a density of the gas, so as to enhance the emission of extremeultra-violet light from the gas.
 6. The method as recited in claim 1wherein the step of flowing a gas at a supersonic velocity comprisesflowing a noble gas at a supersonic velocity.
 7. The method as recitedin claim 1 wherein the step of flowing a gas at a supersonic velocitycomprises flowing, in part, at least an argon gas, helium gas, or xenongas at a supersonic velocity.
 8. The method as recited in claim 1wherein the step of flowing a gas at a supersonic velocity comprisesflowing the gas at a velocity of approximately Mach
 3. 9. The method asrecited in claim 1 wherein the step of flowing a gas at a supersonicvelocity comprises flowing the gas through a vacuum.
 10. The method asrecited in claim 1 wherein the steps of flowing a gas at a supersonicvelocity, directing a radiated energy beam into the flowing gas, andcapturing a substantial portion of the gas are performed substaniallywithin a vacuum.
 11. The method as recited in claim 1 wherein the stepof directing a radiated energy beam into the flowing gas comprisesdirecting an electron beam into the flowing gas.
 12. The method asrecited in claim 1 wherein the step of directing a radiated energy beaminto the flowing gas comprises directing a laser beam into the flowinggas.
 13. The method as recited in claim 1 wherein the step of directinga radiated energy beam into the flowing gas comprises directing amicrowave beam into the flowing gas.
 14. The method as recited in claim1 wherein the step of directing a radiated energy beam into the flowinggas comprises directing the radiated energy beam proximate theconverging-diverging nozzle.
 15. The method as recited in claim 1wherein the step of directing a radiated energy beam into the flowinggas comprises directing the radiated energy beam through the flowing gasin a manner which mitigates absorption of the extreme ultra-violet lightback into the flowing gas.
 16. The method as recited in claim 1 whereinthe step of directing a radiated energy beam into the flowing gascomprises directing the radiated energy beam through the flowing gasproximate a surface of the flowing gas so as to reduce a distance thatthe extreme ultra-violet light must travel through the flowing gas, thusmitigating absorption of the extreme ultra-violet light.
 17. The methodas recited in claim 1 wherein the step of capturing a substantialportion of the gas comprises receiving the substantial portion of thegas within a diffuser, the diffuser being configured to reduce thevelocity of the gas and to increase the pressure of the gas.
 18. Themethod as recited in claim 1 wherein the step of capturing a substantialportion of the gas comprises receiving the substantial portion of thegas within a diffuser having a cross-section approximate to thecross-section of the converging-diverging nozzle.
 19. The method asrecited in claim 1 wherein the step of capturing a substantial portionof the gas comprises receiving the substantial portion of the gas withina diffuser, and pumping a substantial portion of the gas, which is notreceived within the diffuser, via a vacuum pump, so as to facilitaterecycling of the gas.
 20. The method as recited in claim 1 furthercomprising the step of recycling the gas, such that captured gas isrepeatedly flowed at a supersonic velocity and stimulated into emittingextreme ultra-violet light.
 21. The method as recited in claim 1 whereinthe step of capturing a substantial portion of the gas comprisesconverting a substantial portion of a kinetic energy of the gas intopressure, so as to facilitate recycling of the gas.
 22. The method asrecited in claim 1 further comprising the steps of compressing theportion of gas captured and removing heat from the gas catured, so as tofacilitate recycling of the gas.
 23. The method as recited in claim 1wherein the step of capturing a substantial portion of the gas comprisesflowing the gas over at least one knife edge to reduce the velocity ofthe gas.
 24. The method as recited in claim 1 wherein the step ofcapturing a substantial portion of the gas comprises flowing the gasover a plurality of concentric, generally rectangular knife edges. 25.The method as recited in claim 1 wherein the method for producingextreme ultra-violet light is used in the production of a semiconductorcomponent.
 26. A method for producing extreme ultra-violet light in aphotolithography system for production of semiconductor components, themethod comprising:providing a vacuum chamber; flowing a gas through aconverging-diverging nozzle at a supersonic velocity into the vacuumchamber; directing a radiated energy beam into the flowing gas tostimulate emission of extreme ultra violet light from the gas;collecting the extreme ultra-violet light and focusing the extremeultra-violet light so as to facilitate photolithography with the extremeultra-violet light; capturing a substantial portion of the gas so as tomitigate contamination of the collecting and focusing optics thereby,the gas being captured by a diffuser which reduces a velocity of the gasand increases a pressure thereof; and recycling the gas captured by thediffuser to the nozzle such that the captured gas is repeatedly flowedat supersonic velocity and stimulated into emitting extreme ultra-violetlight.
 27. The method as recited in claim 26, wherein the semiconductorcomponent comprises a transistor.
 28. A recycling gas target jet forproducing extreme ultra-violet light comprising:a converging-divergingnozzle for accelerating a gas to form a supersonic jet of gas; and aradiated energy source for providing a radiated energy beam, theradiated energy beam being incident upon the supersoric jet of gas andstimulating extreme ultra-violet light emission from the jet of gas; anda diffuser into which the supersonic jet of gas is directed, thediffuser inlet comprising a diffuser configured to reduce the velocityof the gas and to increase the pressure thereof; wherein the nozzle andthe diffuser inlet are configured to utilize gas dynamics properties ofthe supersonic jet of gas to direct debris formed during interaction ofthe electron beam and the gas jet into the inlet and thus mitigatecontamination of system optical components thereby.
 29. The recyclinggas target jet as recited in claim 28 wherein the converging-divergingnozzle has a generally rectangular cross-section and an aspect ratio ofapproximately 10 to
 1. 30. The recycling gas target jet as recited inclaim 28 wherein the converging-diverging nozzle is configured so as toexpand the gas so as to substantially decrease a temperature of the gas,and thus substantially increase a density of the gas, so as to enhancethe emission of extreme ultra-violet light from the gas.
 31. Therecycling gas target jet as recited in claim 28 wherein the gascomprises a noble gas.
 32. The recycling gas target jet as recited inclaim 28, wherein the gas comprises at least an argon gas, helium gas,or xenon gas.
 33. The recycling gas target jet as recited in claim 28wherein the converging-diverging nozzle comprises a converging-divergingnozzle configured to flow the gas at a velocity at approximately Mach 3.34. The recycling gas target jet as recited in claim 28 furthercomprising a vacuum chamber within which the gas flows.
 35. Therecycling gas target jet as recited in claim 28 wherein the radiatedenergy source comprises an electron beam source.
 36. The recycling gastarget jet as recited in claim 28 wherein the radiated energy sourcecomprises a laser.
 37. The recycling gas target jet as recited in claim28 wherein the radiated energy source comprises a microwave source. 38.The recycling gas target jet as recited in claim 28 wherein the radiatedenergy source is configured to direct the radiated energy beam proximatethe converging-diverging nozzle.
 39. The recycling gas target jet asrecited in claim 28 wherein the radiated energy source is configured todirect the radiated energy beam through the gas in a manner whichmitigates absorption of the extreme ultra-violet light back into theflowing gas.
 40. The recycling gas target jet as recited in claim 28wherein the radiated energy source is configured to direct the radiatedenergy beam through the flowing gas proximate a surface of the flowinggas so as to reduce a distance that extreme ultra-violet light musttravel through the gas, thus mitigating absorption of the extremeultra-violet light.
 41. The recycling gas target jet as recited in claim28 further comprising a diffuser for substantially capturing the gas.42. The recycling gas target jet as recited in claim 28 furthercomprising a vacuum pump for pumping a substantial portion of the gasnot received within the diffuser back to the nozzle, so as to facilitaterecycling of the gas.
 43. The recycling gas target jet as recited inclaim 28 further comprising:a compressor for compressing gas captured bythe diffuser; a heat exchanger for cooling the gas captured by thediffuser; and wherein compressing and cooling the gas captured by thediffuser facilitates recycling of the gas.
 44. The recycling gas targetjet as recited in claim 28 further comprising a plurality of knife edgesformed proximate a diffuser to reduce the velocity of the gas andincrease the pressure of the gas.
 45. An extreme ultra-violet systemcomprising:a vacuum chamber; a nozzle for flowing a gas at a supersonicvelocity into the vacuum chamber; a source of radiated energy fordirecting a radiated energy beam into the flowing gas to stimulateemission of extreme ultra-violet light from the gas; collecting andfocusing optics for collecting the extreme ultra-violet light and forfocusing the extreme ultra-violet light; a diffuser for capturing asubstantial portion of the gas so as to mitigate contamination of thecollecting and focusing optics; and a recycling system for providing gascaptured by the diffuser to the nozzle, such that the gas is repeatedlyused to generate extreme ultra-violet light.